Grant's Victory Carton Illusions book is worth getting, especially if you want to familiarize yourself with the concepts before spending hundreds of dollars. You can pick it up as an ebook for $4.95 here: http://www.trickshop.com/victory_carton_illusions.html
I've worked with two of these in the past (right out of the book)and can say they are extremely practical. A couple of decades ago I was involved with an industrial show for Frigidaire at The Las Vegas Hilton and we did use one of these illusions, with two cardboard boxes, one for a washer and one for a dryer. We produced a Frigidaire executive out of the boxes, the person in charge of that division, so the use of the cardboard boxes fit right in. It was very effective and played well on a huge stage in front of 1,500 people.
One of the best features of these illusions is that you can, with only a few minutes of rehearsal, produce an executive, school principle, or any VIP. For the most part, they only have to stay put and then stand up at the right moment.
As far as the quality of the Creative Magic props goes, I've only heard great things about them. A friend of mine has their Shadow Tent and loves it. I've purchased smaller items from them and they are a good company to deal with.